Shape memory polymers (SMP) are used in the 3D printing field for different applications such as soft robotics or medical devices. Although this technology has expanded the capabilities of additive manufacturing, there still exists fundamental questions regarding the optimum condition for manufacturing these 3D printed parts. Various factors play a crucial role in the final quality of printed parts, such as deposition orientation, percentage infill, or environmental conditions. In this paper, we study the effect of humidity on commercially available SMPs (NinjaFlex©) at both micro- and macro-scale. By performing a 3-dimensional computational fluid dynamic model for the printing environment, it is found there are significant temperature and humidity fluctuations around the hot-end and printing bed. Macro-scale characterization through ASTM D638 tensile testing shows that for humidity levels higher than 60% there is 5-10% reduction in the strength of material (ultimate strength and tangent modulus). This study is verified by micro-scale characterization performed with atomic force microscopy on thin-films. It is shown that in addition to the effect of humidity on the stiffness of materials, there is an effect on the loss moduli of the matter as well. As humidity increases, these polymers become more viscoelastic. Simultaneously, it is shown higher humidity levels cause increased micro-level surface roughness, which can be the cause for the strength reduction for higher humidities.

Additive manufacturing has become a widely utilized process in industrial, academic, and household applications. Previous studies have demonstrated that non-optimum humidity conditions can adversely impact the print quality of parts printed from plastic filaments by changing their mechanical properties, such as elastic modulus and ultimate strength. This study utilized a computational fluid dynamics (CFD) approach and experimental testing to design a system that yields a more uniform humidity distribution in a 3-dimensional (3D) printer printing region. The study resulted in an optimized enclosure with significantly higher relative humidity (RH) uniformity in the print volume. The simulations predicted that the optimized enclosure would improve the uniformity by about 65%, while experimental testing pointed to even more significant improvement at about 75%. As a case study, tensile testing of 3D printed specimens made from NinjaFlex© filamenets under the optimum environmental conditions showed 11% higher ultimate strength and more elastic behavior than specimens printed using the baseline model.

Additive manufacturing has become a widely utilized process in industrial, academic, and household applications. Previous studies have demonstrated that non-optimum humidity conditions can adversely impact the print quality of parts printed from plastic filaments by changing their mechanical properties, such as elastic modulus and ultimate strength. This study utilized a computational fluid dynamics (CFD) approach and experimental testing to design a system that yields a more uniform humidity distribution in a 3-dimensional (3D) printer printing region. The study resulted in an optimized enclosure with significantly higher relative humidity (RH) uniformity in the print volume. The simulations predicted that the optimized enclosure would improve the uniformity by about 65%, while experimental testing pointed to even more significant improvement at about 75%. As a case study, tensile testing of 3D printed specimens made from NinjaFlex© filamenets under the optimum environmental conditions showed 11% higher ultimate strength and more elastic behavior than specimens printed using the baseline model.